The release paper or film is obtained by coating a curable silicone composition as silicone-base release agent to the surface of substrates such as plastic film or paper, and effecting crosslinking reaction to form a cured coating. The resulting coating is widely used as a release agent layer relative to adhesive or pressure-sensitive adhesive (PSA) substances.
Among these curable silicone compositions, silicone compositions of addition reaction type adapted to cure via hydrosilylation reaction are well known, for example, a silicone composition comprising an alkenyl-containing organopolysiloxane, an organohydrogenpolysiloxane, and a platinum base compound, as disclosed in JP-A S62-86061 (Patent Document 1). Since this composition has advantages including a high cure rate, a good pot-life, and widely varying release properties, it is widely used as the silicone release agent.
Under the recent trend of available substrates, the use of plastic film substrates is increasing because of uniform and stable quality, high smoothness, and possible film thickness reduction. The drawback of plastic film substrates is poor heat resistance as compared with paper. Therefore, the heating temperature during formation of a cured coating of silicone composition is limited. Since extremely high temperature curing is prohibited, there has hitherto been a strong demand for an improvement in curing of silicone compositions.
As to paper substrates, a variety of composite substrates having paper combined with plastic materials have been developed for the purpose of imparting a function which is not achievable solely with paper. Not only conventional PE-laminated paper, but also a wide variety of substrates are used. Many composite substrates suffer from heat resistance like plastic film substrates. In addition, there are recently increasing applications where higher performance is required with respect to dimensional stability, processing accuracy, transparency, and reflection properties. There is a strong propensity to avoid the likelihood of deformation and appearance degradation by heating. The demand for improvements in curing of silicone compositions is increasing.
Proposals for improving the cure of silicone compositions were made from the past. As the method for making modifications to the base polymer structure in silicone compositions, for example, JP-A S63-251465, JP-B H03-19267, JP-A H09-78032, and JP-A H11-193366 (Patent Documents 2 to 5) propose to incorporate a branched structure containing RSiO3/2 units wherein R is a monovalent hydrocarbon group. Since these methods intend to reduce the release force upon high-speed peeling and to improve cure, the improvement in cure is observable merely as an auxiliary effect.
Also JP-A S60-190458 (Patent Document 6) proposes to change the arrangement and structure of functional groups on a base polymer in a silicone composition. With respect to cure, there is a need for further improvement.
With respect to release properties, on the other hand, cured coatings of silicone compositions receive high reputation from the past. In the recent years, a lighter release is required to comply with improvements in the performance of pressure-sensitive adhesive and adhesive, and diversification of applications. Particularly in the mold parting film application, there is a tendency that the cured coating of silicone composition becomes thinner, indicating a transition toward the situation that fails to take full advantage of the mold parting of the cured coating.
As discussed above, there is not found in the prior art an appropriate method capable of improving the cure of a silicone composition while improving the mold parting of a cured coating thereof. Thus there is a demand for a silicone composition capable of meeting both light release property and high curability.